Optimal parameter for the SOR-like iteration method for solving the system of absolute value equations

Abstract

The SOR-like iteration method for solving the absolute value equations~(AVE) of finding a vector $x$ such that $Ax - |x| - b = 0$ with $ν= \|A^{-1}\|_2 < 1$ is investigated. The convergence conditions of the SOR-like iteration method proposed by Ke and Ma ([{\em Appl. Math. Comput.}, 311:195--202, 2017]) are revisited and a new proof is given, which exhibits some insights in determining the convergent region and the optimal iteration parameter. Along this line, the optimal parameter which minimizes $\|T_ν(ω)\|_2$ with $$T_ν(ω) = \left(\begin{array}{cc} |1-ω| & ω^2ν\\ |1-ω| & |1-ω| +ω^2ν\end{array}\right)$$ and the approximate optimal parameter which minimizes $η_ν(ω) =\max\{|1-ω|,νω^2\}$ are explored. The optimal and approximate optimal parameters are iteration-independent and the bigger value of $ν$ is, the smaller convergent region of the iteration parameter $ω$ is. Numerical results are presented to demonstrate that the SOR-like iteration method with the optimal parameter is superior to that with the approximate optimal parameter proposed by Guo, Wu and Li ([{\em Appl. Math. Lett.}, 97:107--113, 2019]). In some situation, the SOR-like itration method with the optimal parameter performs better, in terms of CPU time, than the generalized Newton method (Mangasarian, [{\em Optim. Lett.}, 3:101--108, 2009]) for solving the AVE.